Add workflow trigger for testing docker image per PR

Author: polRk

Diff for: .github/workflows/docker_publish.yml renamed to .github/workflows/docker_build_test_publish.yml

@@ -1,8 +1,11 @@
-name: Publish docker image
+name: Build, Test, Publish docker image
 
 on:
   schedule:
     - cron: "0 3 * * *"  # At 03:00 every day
+  pull_request_target:
+    branches:
+      - 'main'
   workflow_dispatch:
     inputs:
       git_ref:
@@ -102,6 +105,7 @@ jobs:
           docker stop local-ydb-test || true
 
       - name: Push docker image
+        if: ${{ github.event_name != 'pull_request_target' }}
         uses: docker/build-push-action@v4
         with:
           context: .